The invention relates to the manufacture of data storage media such as optical data storage disks.
Optical media such as optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. Optical data storage disks include, for example, audio CD (compact disc), CD-R (CD-recordable), CD-ROM (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (DVD-random access memory), and various types of rewritable media, such as magneto-optical (MO) disks and phase change optical disks. Some newer formats for optical data storage disks have storage capabilities on both sides of the disk. In addition, some newer formats are progressing toward smaller disk sizes.
Optical data storage disks can be produced by first making a master that has a surface pattern that represents encoded data on the master surface. The surface pattern, for instance, may be a collection of grooves that define master pits and master lands. The master is typically created by a relatively expensive mastering process. After creating a suitable master, that master can then be used to make a stamper. The stamper has a surface pattern that is the inverse of the surface pattern encoded on the master. The stamper, then, can be used to stamp large quantities of replica disks in a mass production stamping process, such as a rolling bead process like that taught by the current inventor in U.S. Pat. No. 4,374,077.
In a rolling bead process, a bead of photopolymer is positioned between a substrate and the stamper. A roller passes over the substrate and the stamper, dispersing the bead of photopolymer and forcing air to the leading edge of the bead. After the roller has passed over the substrate and the stamper and dispersed the photopolymer, the photopolymer can be cured with ultraviolet (UV) light. The stamper is then peeled back, leaving an inverted image of the stamper within the photopolymer that is cured to the substrate. A reflective material, a phase change material, a magneto-optic material, or the like can then be deposited on the photopolymer. Additional protective layers may also be added.
In general, the invention is directed toward techniques for creating optical data storage disks. In particular, the invention is directed toward techniques for creating two-sided optical data storage disks, or in other words, disks capable of storing information on both sides. In some embodiments, the techniques can be used to create two-sided, dual-layer optical data storage disks. In those cases, two layers of information can be stored on both sides of the disks.
In one embodiment, the invention provides a simultaneous two-sided rolling bead process. For example, a method may include positioning a first bead of photopolymer for distribution between a bottom stamper and a substrate, and positioning a second bead of photopolymer for distribution between a top stamper and the substrate. The method may also include passing a roller over the top stamper to distribute the beads of photopolymer, curing the photopolymer, and removing the substrate from the stampers.
The cured layers of photopolymer on both sides of the substrate define information layers on the medium. Materials can be deposited on the information layers according to a media format. For example, phase change materials, magneto-optic materials or reflective materials can be deposited, depending on the type of medium being created. Reflective materials can be used to define read-only formats, or alternatively phase change materials or magneto-optic materials can be used to define write-once or re-writable formats.
The simultaneous two-sided rolling bead process may be repeated to create additional information layers on both sides of the medium. For example, in one embodiment, a first simultaneous two-sided rolling bead process can be followed by the deposition of phase change material. Then, a second simultaneous two-sided rolling bead process can be applied to the same medium, followed by the deposition of reflective material. The outer reflective layers defined by the reflective material may be semi-transparent so that some light can penetrate through the reflective layers. This can ensure that the phase change materials deposited on the inner information layers can be optically changed and/or optically detected by a disk drive.
In two-sided dual-layer media, the outer information layers may need to be sufficiently thick to avoid optical interference between information stored on the outer layer and information stored on the inner layer on the same side of the medium. In other words, material deposited on the outer information layer may need to be a sufficient distance from material deposited on the inner information layer to ensure that an optical drive is able to focus light on the surface of the inner information layer without interference from outer information layer. The viscosity of the photopolymer that is used to create the information layers can be predetermined to control the thicknesses of the information layers. For example, the photopolymers used in the simultaneous two-sided rolling bead processes can be made to have a sufficiently high viscosity so that information layers have appropriate thicknesses. In particular, outer information layers may need thicknesses on the order of 50 microns or greater.
The invention provides several advantages. For example, the invention can be used to realize optical data storage disks having increased data storage capacities. Moreover, the invention can be used to realize hybrid data storage disks having both read-only format and write-once or re-writable formats on both sides of the disk. Disks having both read-only formats and re-writable formats are particularly useful for applications where some information needs to be permanently stored while other information can be stored and then discarded or replaced.
The techniques according to the invention also provide advantages in optimizing information layer thicknesses. In particular, for two-sided dual-layer disks, the thickness of the outer information layers may need to be sufficiently thick to avoid interference between material deposited on the respective information layers on the same side of the disk. By predetermining the viscosity of the photopolymers used, the invention provides a relatively simple way to control information layer thicknesses. The pressure and rolling speed of the roller used in the simultaneous two-sided rolling bead processes can also be controlled to define information layer thicknesses. Thicknesses on the order of 50 microns for the outer information layers may be sufficient to avoid interference.
Another advantage can be realized by utilizing oversized disks during the two-sided rolling bead processes and then die punching the oversized disks to size. This can avoid problems associated with thickness variations at the outer edges of the oversized disk that may be present if the substrate is an injection molded substrate. The invention also provides advantages over other methods of creating two-sided dual-layer optical data storage disks. In particular, conventional spin coating techniques may be ineffective in creating uniform information layer thicknesses for the outer layers of dual-layer disks. Moreover, because spin coating techniques utilize the effects of gravity in the coating process, spin coating techniques typically require each side of the disk to be spin coated independently. This can lead to disk imperfections and thickness variations of the spin coated photopolymer. The two-sided rolling bead processes according to the invention, however, are not limited in this manner.
Additional details of these and other embodiments are set forth in the accompanying drawings and the description below. Other features, objects and advantages will become apparent from the description and drawings, and from the claims.